Wednesday, May 25, 2016

Black Hole Tore Apart and Swallowed a Star

Sun-like stars, white dwarfs and giant stars can be wholly swallowed by black holes with masses greater than ~100 million, ~100 thousand and ~10 billion times the mass of the Sun, respectively. When a star is wholly swallowed by a black hole, no flares will be observed. In contrast, for a black hole that is not massive enough to swallow a star whole, a tidal disruption flare can be generated. A star approaching such a black hole on a low angular momentum orbit can be torn apart by tidal forces and a fraction of the star's mass can form an accretion disk around the black hole, powering a tidal disruption flare.

XMMSL1J063045.9603110 is a candidate tidal disruption event. This event was first detected in X-rays with an underlying soft X-ray thermal emission. Twenty days later, XMMSL1J063045.9603110 was again detected with soft X-ray thermal emission, this time ~10 times dimmer than when it was first detected. The X-ray emission over time appears to be consistent with the presence of an accretion disk around a black hole. In this case, the accretion disk represents a fraction of the material left over from a tidally disrupted star that got swallowed by the black hole.Depending on assumptions, the black hole responsible for this tidal disruption flare is estimated to have between ~10 thousand to ~100 thousand times the mass of the Sun. Optical observations suggest that the black hole associated with XMMSL1J063045.9-603110 likely resides within either a very faint dwarf galaxy or a very bright globular cluster. If the black hole resides within a globular cluster, then XMMSL1J063045.9-603110 could be the first tidal disruption flare observed in a globular cluster.Reference:Mainetti et al. (2016), "XMMSL1J063045.9-603110: a tidal disruption event fallen into the back burner", arXiv:1605.06133 [astro-ph.HE]